linux/mm/slob.c
Nick Piggin 553948491c slob: improved alignment handling
Remove the core slob allocator's minimum alignment restrictions, and instead
introduce the alignment restrictions at the slab API layer.  This lets us heed
the ARCH_KMALLOC/SLAB_MINALIGN directives, and also use __alignof__ (unsigned
long) for the default alignment (which should allow relaxed alignment
architectures to take better advantage of SLOB's small minimum alignment).

Signed-off-by: Nick Piggin <npiggin@suse.de>
Acked-by: Matt Mackall <mpm@selenic.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
2007-07-16 09:05:35 -07:00

602 lines
14 KiB
C

/*
* SLOB Allocator: Simple List Of Blocks
*
* Matt Mackall <mpm@selenic.com> 12/30/03
*
* How SLOB works:
*
* The core of SLOB is a traditional K&R style heap allocator, with
* support for returning aligned objects. The granularity of this
* allocator is as little as 2 bytes, however typically most architectures
* will require 4 bytes on 32-bit and 8 bytes on 64-bit.
*
* The slob heap is a linked list of pages from __get_free_page, and
* within each page, there is a singly-linked list of free blocks (slob_t).
* The heap is grown on demand and allocation from the heap is currently
* first-fit.
*
* Above this is an implementation of kmalloc/kfree. Blocks returned
* from kmalloc are prepended with a 4-byte header with the kmalloc size.
* If kmalloc is asked for objects of PAGE_SIZE or larger, it calls
* __get_free_pages directly, allocating compound pages so the page order
* does not have to be separately tracked, and also stores the exact
* allocation size in page->private so that it can be used to accurately
* provide ksize(). These objects are detected in kfree() because slob_page()
* is false for them.
*
* SLAB is emulated on top of SLOB by simply calling constructors and
* destructors for every SLAB allocation. Objects are returned with the
* 4-byte alignment unless the SLAB_HWCACHE_ALIGN flag is set, in which
* case the low-level allocator will fragment blocks to create the proper
* alignment. Again, objects of page-size or greater are allocated by
* calling __get_free_pages. As SLAB objects know their size, no separate
* size bookkeeping is necessary and there is essentially no allocation
* space overhead, and compound pages aren't needed for multi-page
* allocations.
*/
#include <linux/kernel.h>
#include <linux/slab.h>
#include <linux/mm.h>
#include <linux/cache.h>
#include <linux/init.h>
#include <linux/module.h>
#include <linux/rcupdate.h>
#include <linux/list.h>
#include <asm/atomic.h>
/*
* slob_block has a field 'units', which indicates size of block if +ve,
* or offset of next block if -ve (in SLOB_UNITs).
*
* Free blocks of size 1 unit simply contain the offset of the next block.
* Those with larger size contain their size in the first SLOB_UNIT of
* memory, and the offset of the next free block in the second SLOB_UNIT.
*/
#if PAGE_SIZE <= (32767 * 2)
typedef s16 slobidx_t;
#else
typedef s32 slobidx_t;
#endif
struct slob_block {
slobidx_t units;
};
typedef struct slob_block slob_t;
/*
* We use struct page fields to manage some slob allocation aspects,
* however to avoid the horrible mess in include/linux/mm_types.h, we'll
* just define our own struct page type variant here.
*/
struct slob_page {
union {
struct {
unsigned long flags; /* mandatory */
atomic_t _count; /* mandatory */
slobidx_t units; /* free units left in page */
unsigned long pad[2];
slob_t *free; /* first free slob_t in page */
struct list_head list; /* linked list of free pages */
};
struct page page;
};
};
static inline void struct_slob_page_wrong_size(void)
{ BUILD_BUG_ON(sizeof(struct slob_page) != sizeof(struct page)); }
/*
* free_slob_page: call before a slob_page is returned to the page allocator.
*/
static inline void free_slob_page(struct slob_page *sp)
{
reset_page_mapcount(&sp->page);
sp->page.mapping = NULL;
}
/*
* All (partially) free slob pages go on this list.
*/
static LIST_HEAD(free_slob_pages);
/*
* slob_page: True for all slob pages (false for bigblock pages)
*/
static inline int slob_page(struct slob_page *sp)
{
return test_bit(PG_active, &sp->flags);
}
static inline void set_slob_page(struct slob_page *sp)
{
__set_bit(PG_active, &sp->flags);
}
static inline void clear_slob_page(struct slob_page *sp)
{
__clear_bit(PG_active, &sp->flags);
}
/*
* slob_page_free: true for pages on free_slob_pages list.
*/
static inline int slob_page_free(struct slob_page *sp)
{
return test_bit(PG_private, &sp->flags);
}
static inline void set_slob_page_free(struct slob_page *sp)
{
list_add(&sp->list, &free_slob_pages);
__set_bit(PG_private, &sp->flags);
}
static inline void clear_slob_page_free(struct slob_page *sp)
{
list_del(&sp->list);
__clear_bit(PG_private, &sp->flags);
}
#define SLOB_UNIT sizeof(slob_t)
#define SLOB_UNITS(size) (((size) + SLOB_UNIT - 1)/SLOB_UNIT)
#define SLOB_ALIGN L1_CACHE_BYTES
/*
* struct slob_rcu is inserted at the tail of allocated slob blocks, which
* were created with a SLAB_DESTROY_BY_RCU slab. slob_rcu is used to free
* the block using call_rcu.
*/
struct slob_rcu {
struct rcu_head head;
int size;
};
/*
* slob_lock protects all slob allocator structures.
*/
static DEFINE_SPINLOCK(slob_lock);
/*
* Encode the given size and next info into a free slob block s.
*/
static void set_slob(slob_t *s, slobidx_t size, slob_t *next)
{
slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
slobidx_t offset = next - base;
if (size > 1) {
s[0].units = size;
s[1].units = offset;
} else
s[0].units = -offset;
}
/*
* Return the size of a slob block.
*/
static slobidx_t slob_units(slob_t *s)
{
if (s->units > 0)
return s->units;
return 1;
}
/*
* Return the next free slob block pointer after this one.
*/
static slob_t *slob_next(slob_t *s)
{
slob_t *base = (slob_t *)((unsigned long)s & PAGE_MASK);
slobidx_t next;
if (s[0].units < 0)
next = -s[0].units;
else
next = s[1].units;
return base+next;
}
/*
* Returns true if s is the last free block in its page.
*/
static int slob_last(slob_t *s)
{
return !((unsigned long)slob_next(s) & ~PAGE_MASK);
}
/*
* Allocate a slob block within a given slob_page sp.
*/
static void *slob_page_alloc(struct slob_page *sp, size_t size, int align)
{
slob_t *prev, *cur, *aligned = 0;
int delta = 0, units = SLOB_UNITS(size);
for (prev = NULL, cur = sp->free; ; prev = cur, cur = slob_next(cur)) {
slobidx_t avail = slob_units(cur);
if (align) {
aligned = (slob_t *)ALIGN((unsigned long)cur, align);
delta = aligned - cur;
}
if (avail >= units + delta) { /* room enough? */
slob_t *next;
if (delta) { /* need to fragment head to align? */
next = slob_next(cur);
set_slob(aligned, avail - delta, next);
set_slob(cur, delta, aligned);
prev = cur;
cur = aligned;
avail = slob_units(cur);
}
next = slob_next(cur);
if (avail == units) { /* exact fit? unlink. */
if (prev)
set_slob(prev, slob_units(prev), next);
else
sp->free = next;
} else { /* fragment */
if (prev)
set_slob(prev, slob_units(prev), cur + units);
else
sp->free = cur + units;
set_slob(cur + units, avail - units, next);
}
sp->units -= units;
if (!sp->units)
clear_slob_page_free(sp);
return cur;
}
if (slob_last(cur))
return NULL;
}
}
/*
* slob_alloc: entry point into the slob allocator.
*/
static void *slob_alloc(size_t size, gfp_t gfp, int align)
{
struct slob_page *sp;
slob_t *b = NULL;
unsigned long flags;
spin_lock_irqsave(&slob_lock, flags);
/* Iterate through each partially free page, try to find room */
list_for_each_entry(sp, &free_slob_pages, list) {
if (sp->units >= SLOB_UNITS(size)) {
b = slob_page_alloc(sp, size, align);
if (b)
break;
}
}
spin_unlock_irqrestore(&slob_lock, flags);
/* Not enough space: must allocate a new page */
if (!b) {
b = (slob_t *)__get_free_page(gfp);
if (!b)
return 0;
sp = (struct slob_page *)virt_to_page(b);
set_slob_page(sp);
spin_lock_irqsave(&slob_lock, flags);
sp->units = SLOB_UNITS(PAGE_SIZE);
sp->free = b;
INIT_LIST_HEAD(&sp->list);
set_slob(b, SLOB_UNITS(PAGE_SIZE), b + SLOB_UNITS(PAGE_SIZE));
set_slob_page_free(sp);
b = slob_page_alloc(sp, size, align);
BUG_ON(!b);
spin_unlock_irqrestore(&slob_lock, flags);
}
return b;
}
/*
* slob_free: entry point into the slob allocator.
*/
static void slob_free(void *block, int size)
{
struct slob_page *sp;
slob_t *prev, *next, *b = (slob_t *)block;
slobidx_t units;
unsigned long flags;
if (!block)
return;
BUG_ON(!size);
sp = (struct slob_page *)virt_to_page(block);
units = SLOB_UNITS(size);
spin_lock_irqsave(&slob_lock, flags);
if (sp->units + units == SLOB_UNITS(PAGE_SIZE)) {
/* Go directly to page allocator. Do not pass slob allocator */
if (slob_page_free(sp))
clear_slob_page_free(sp);
clear_slob_page(sp);
free_slob_page(sp);
free_page((unsigned long)b);
goto out;
}
if (!slob_page_free(sp)) {
/* This slob page is about to become partially free. Easy! */
sp->units = units;
sp->free = b;
set_slob(b, units,
(void *)((unsigned long)(b +
SLOB_UNITS(PAGE_SIZE)) & PAGE_MASK));
set_slob_page_free(sp);
goto out;
}
/*
* Otherwise the page is already partially free, so find reinsertion
* point.
*/
sp->units += units;
if (b < sp->free) {
set_slob(b, units, sp->free);
sp->free = b;
} else {
prev = sp->free;
next = slob_next(prev);
while (b > next) {
prev = next;
next = slob_next(prev);
}
if (!slob_last(prev) && b + units == next) {
units += slob_units(next);
set_slob(b, units, slob_next(next));
} else
set_slob(b, units, next);
if (prev + slob_units(prev) == b) {
units = slob_units(b) + slob_units(prev);
set_slob(prev, units, slob_next(b));
} else
set_slob(prev, slob_units(prev), b);
}
out:
spin_unlock_irqrestore(&slob_lock, flags);
}
/*
* End of slob allocator proper. Begin kmem_cache_alloc and kmalloc frontend.
*/
#ifndef ARCH_KMALLOC_MINALIGN
#define ARCH_KMALLOC_MINALIGN __alignof__(unsigned long)
#endif
#ifndef ARCH_SLAB_MINALIGN
#define ARCH_SLAB_MINALIGN __alignof__(unsigned long)
#endif
void *__kmalloc(size_t size, gfp_t gfp)
{
int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
if (size < PAGE_SIZE - align) {
unsigned int *m;
m = slob_alloc(size + align, gfp, align);
if (m)
*m = size;
return (void *)m + align;
} else {
void *ret;
ret = (void *) __get_free_pages(gfp | __GFP_COMP,
get_order(size));
if (ret) {
struct page *page;
page = virt_to_page(ret);
page->private = size;
}
return ret;
}
}
EXPORT_SYMBOL(__kmalloc);
/**
* krealloc - reallocate memory. The contents will remain unchanged.
*
* @p: object to reallocate memory for.
* @new_size: how many bytes of memory are required.
* @flags: the type of memory to allocate.
*
* The contents of the object pointed to are preserved up to the
* lesser of the new and old sizes. If @p is %NULL, krealloc()
* behaves exactly like kmalloc(). If @size is 0 and @p is not a
* %NULL pointer, the object pointed to is freed.
*/
void *krealloc(const void *p, size_t new_size, gfp_t flags)
{
void *ret;
if (unlikely(!p))
return kmalloc_track_caller(new_size, flags);
if (unlikely(!new_size)) {
kfree(p);
return NULL;
}
ret = kmalloc_track_caller(new_size, flags);
if (ret) {
memcpy(ret, p, min(new_size, ksize(p)));
kfree(p);
}
return ret;
}
EXPORT_SYMBOL(krealloc);
void kfree(const void *block)
{
struct slob_page *sp;
if (!block)
return;
sp = (struct slob_page *)virt_to_page(block);
if (slob_page(sp)) {
int align = max(ARCH_KMALLOC_MINALIGN, ARCH_SLAB_MINALIGN);
unsigned int *m = (unsigned int *)(block - align);
slob_free(m, *m + align);
} else
put_page(&sp->page);
}
EXPORT_SYMBOL(kfree);
/* can't use ksize for kmem_cache_alloc memory, only kmalloc */
size_t ksize(const void *block)
{
struct slob_page *sp;
if (!block)
return 0;
sp = (struct slob_page *)virt_to_page(block);
if (slob_page(sp))
return ((slob_t *)block - 1)->units + SLOB_UNIT;
else
return sp->page.private;
}
struct kmem_cache {
unsigned int size, align;
unsigned long flags;
const char *name;
void (*ctor)(void *, struct kmem_cache *, unsigned long);
};
struct kmem_cache *kmem_cache_create(const char *name, size_t size,
size_t align, unsigned long flags,
void (*ctor)(void*, struct kmem_cache *, unsigned long),
void (*dtor)(void*, struct kmem_cache *, unsigned long))
{
struct kmem_cache *c;
c = slob_alloc(sizeof(struct kmem_cache), flags, 0);
if (c) {
c->name = name;
c->size = size;
if (flags & SLAB_DESTROY_BY_RCU) {
/* leave room for rcu footer at the end of object */
c->size += sizeof(struct slob_rcu);
}
c->flags = flags;
c->ctor = ctor;
/* ignore alignment unless it's forced */
c->align = (flags & SLAB_HWCACHE_ALIGN) ? SLOB_ALIGN : 0;
if (c->align < ARCH_SLAB_MINALIGN)
c->align = ARCH_SLAB_MINALIGN;
if (c->align < align)
c->align = align;
} else if (flags & SLAB_PANIC)
panic("Cannot create slab cache %s\n", name);
return c;
}
EXPORT_SYMBOL(kmem_cache_create);
void kmem_cache_destroy(struct kmem_cache *c)
{
slob_free(c, sizeof(struct kmem_cache));
}
EXPORT_SYMBOL(kmem_cache_destroy);
void *kmem_cache_alloc(struct kmem_cache *c, gfp_t flags)
{
void *b;
if (c->size < PAGE_SIZE)
b = slob_alloc(c->size, flags, c->align);
else
b = (void *)__get_free_pages(flags, get_order(c->size));
if (c->ctor)
c->ctor(b, c, 0);
return b;
}
EXPORT_SYMBOL(kmem_cache_alloc);
void *kmem_cache_zalloc(struct kmem_cache *c, gfp_t flags)
{
void *ret = kmem_cache_alloc(c, flags);
if (ret)
memset(ret, 0, c->size);
return ret;
}
EXPORT_SYMBOL(kmem_cache_zalloc);
static void __kmem_cache_free(void *b, int size)
{
if (size < PAGE_SIZE)
slob_free(b, size);
else
free_pages((unsigned long)b, get_order(size));
}
static void kmem_rcu_free(struct rcu_head *head)
{
struct slob_rcu *slob_rcu = (struct slob_rcu *)head;
void *b = (void *)slob_rcu - (slob_rcu->size - sizeof(struct slob_rcu));
__kmem_cache_free(b, slob_rcu->size);
}
void kmem_cache_free(struct kmem_cache *c, void *b)
{
if (unlikely(c->flags & SLAB_DESTROY_BY_RCU)) {
struct slob_rcu *slob_rcu;
slob_rcu = b + (c->size - sizeof(struct slob_rcu));
INIT_RCU_HEAD(&slob_rcu->head);
slob_rcu->size = c->size;
call_rcu(&slob_rcu->head, kmem_rcu_free);
} else {
__kmem_cache_free(b, c->size);
}
}
EXPORT_SYMBOL(kmem_cache_free);
unsigned int kmem_cache_size(struct kmem_cache *c)
{
return c->size;
}
EXPORT_SYMBOL(kmem_cache_size);
const char *kmem_cache_name(struct kmem_cache *c)
{
return c->name;
}
EXPORT_SYMBOL(kmem_cache_name);
int kmem_cache_shrink(struct kmem_cache *d)
{
return 0;
}
EXPORT_SYMBOL(kmem_cache_shrink);
int kmem_ptr_validate(struct kmem_cache *a, const void *b)
{
return 0;
}
void __init kmem_cache_init(void)
{
}